Field of the Invention
The invention relates to an inking unit in a printing machine, which includes a screen roller and an ink metering system subdivided into inking zones and assigned to the screen roller for zonal ink metering occurring on the latter.
The published German Patent Document DE 41 08 883 A1 describes such an inking unit, which has a doctor blade provided with temperature control devices and cooperating with the screen roller. The doctor blade is subdivided into thermally insulated zones, each of which is heatable selectively by one of the temperature control devices, so that temperature profiling of the doctor blade takes place. In this inking unit, the doctor blade with the temperature control devices thereof functions as an ink metering system by which a printing ink is supplied in different layer thicknesses to a printing material web, and consequently produce different color tones or shades on the latter.
A disadvantage of this heretofore known inking unit is that it is suitable only for inks having a viscosity which is highly temperature-dependent.
Inking units further known in the prior art are described in the documents cited hereinbelow.
The European Patent Document EP 0 315 09 B1 describes an inking unit having a chambered doctor blade, in the ink distribution chamber of which a single profiled element is pivotably arranged.
The European Patent Documents DE 37 04 433 C2 and DE 38 00 411 C2 (EP 0 324 141 B1) describe inking units with a chambered doctor blade having an antechamber.
None of the inking units described in the aforecited documents permit a zonally different ink metering of a printing ink having a viscosity that is of low temperature dependence.
The published European Patent Document EP 0 752 311 B1 describes an inking unit which does not correspond to the generic type described in the introduction hereto, this inking unit having an ink metering system subdivided into inking zones and assigned to an ink duct roller, the metering system comprising a metering roller engageable by a metering doctor blade and being formed with fine recesses on the circumferential surface thereof for receiving printing ink therein.
Further pertinent prior art is described in an article entitled xe2x80x9cRasterwalzenauftragsverfahren mit Druckkammerrakel ein Beschichtungswerkzeug auch fxc3xcr strahlungschemisch hxc3xa4rtende Systemexe2x80x9d (xe2x80x9cScreen-roller application method using pressurized chambered doctor bladesxe2x80x94a coating tool also for systems curing by radiation chemistryxe2x80x9d) by Dr W. Neumann, printed in the journal xe2x80x9cCoatingxe2x80x9d, Issue December 1996, the article referring to a presentation made at the 21st Mxc3xcnich Gluing and Finishing Seminar, and mentioning line screen rollers.
Starting from the aforementioned prior art, it is an object of the invention to provide an inking unit of the general type described at the introduction hereto which is also suitable for printing inks having a viscosity that is comparatively minimally temperature-dependent.
With the foregoing and other objects in view, there is provided, in accordance with one aspect of the invention, an inking unit in a printing machine, comprising a screen roller and an ink metering system subdivided into inking zones and assigned to the screen roller for performing zonal ink metering on the screen roller, the ink metering system having metering elements disposed so as to be movable relative to one another.
In accordance with another feature of the invention, the inking unit includes a chambered doctor blade unit bearing on the screen roller, the doctor blade unit having a working doctor blade and a closing doctor blade.
In accordance with a further feature of the invention, the metering elements are disposed in an ink chamber formed in the chambered doctor blade unit.
In accordance with an added feature of the invention, the metering elements are disposed at locations selected from the group thereof consisting of close to and on the working doctor blade.
In accordance with an additional feature of the invention, the inking unit includes an antechamber provided at a location selected from the group thereof consisting of close to and on the closing doctor blade.
In accordance with yet another feature of the invention, the antechamber narrows at an acute wedge angle towards the closing doctor blade.
In accordance with yet a further feature of the invention, the antechamber has a widened chamber section located between an inlet gap and an overflow channel.
In accordance with yet an added feature of the invention, the inking unit includes an adjustable throttle valve assigned to the chambered doctor blade at an outlet side thereof.
In accordance with yet an additional feature of the invention, the screen roller is formed with a helical line screen.
In accordance with a concomitant aspect of the invention, there is provided a printing machine having an inking unit comprising a screen roller and an ink metering system subdivided into inking zones and assigned to the screen roller for zonal ink metering performable on the screen roller, the ink metering system having metering elements disposed so as to be movable relative to one another.
Each of the metering elements is assigned to one of the inking zones and controls the ink supply into the respective inking zone. By manual or motorized adjustment of the metering elements in relation to one another, a different metered quantity of the printing ink can be set in each of the inking zones. The printing ink, in terms of the viscosity thereof, can be temperature-dependent only to a comparatively little extent.
The inking unit according to the invention is particularly well suited for use in a flexographic printing unit.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in an inking unit in a printing machine, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, wherein: